Electrically operated corner steadies are widely used in modern caravans with remote-controlled drive units. Examples of electrically powered corner steadies are disclosed in U.S. Pat. No. 4,103,869 and EP 1 257 450. A battery in the caravan powers a DC electric motor through an electric circuit in each drive unit. The output shaft of the electric motor is connected to the screw spindle which is provided with a moving nut for actuating and moving a support leg of the steady between a folded rest position and an extended support position of the leg. The nut is usually linked to one end of an arm or strut which in turn is linked at its opposite end to the support leg.
When the leg reaches an extreme position, for example the folded rest position, or the nut reaches the end of the thread of the spindle, the nut cannot move any farther on the spindle. However, normally power is continuously supplied to the motor resulting in continuous rotation of spindle and a steep rise in torque in the spindle due to the power characteristic of the electric motor. At these positions, the friction between nut and spindle may become so high that nut will get stuck on the thread of spindle as the spindle is still forced to rotate by the motor, eventually locking the nut on the spindle. If the spindle becomes stuck at these positions, the nut/spindle engagement may be locked such that the motor cannot overcome the friction and release the spindle from the locked engagement by reversing the direction of rotation of the spindle. If this situation arises, the motor and thus the drive unit of corner steady will fail.
A known solution to this problem is to provide the motor with an overload protection such that when current through the motor exceeds a predetermined value, the power supply is interrupted. However, in order for the overload protection to have time to react when the nut reaches an end position or cannot move for other reasons, the spindle is provided with a low rotational speed by the motor/gearbox which in turn results in an extended time for moving the support leg. This extended operational time for moving the leg is of course not desirable.